Abstract

The Petani Field in Central Sumatra was discovered in 1964. To date, the field has produced over 293 million barrels of oil with the "Menggala-3900'Sand" as the main producing reservoir. The recommendation to drill a horizontal well through this reservoir was approved in 1992. The twofold purpose was to minimize water coning and improve ultimate recovery. The geological work required to support the project included detailed reservoir evaluation, geological mapping, drilling program preparation and evaluation while drilling.

The target zone ("A" interval) covers an area 700 meters by 2,000 meters with the oil pay thickness ranging from 20 to 45 feet. Evaluation of the target size, geologic structure, present oil isopach and available drilling technology led to the decision to drill two horizontal wells. Reservoir and oil pay thickness and reservoir quality distribution were major factors in guiding the decision to have a "15-foot target window". Critical geology related factors required to prepare a horizontal well drilling program are reservoir target and planned horizontal section. Finally, the horizontal target represents a path that is expected to track the structural configuration and most appropriate reservoir quality.

P.T.Caltex Pacific Indonesia has successfully drilled and completed its very first two horizontal wells in the Petani Field. Top reservoir target and target windows were encountered as programmed. Each well penetrated about 2,000 feet of horizontal section. This success proved the critical and important role of local geologic knowledge in preparing and executing a horizontal well drilling program.